1. Field of the Invention
The present invention relates to a current supplying system, an ADC utilizing the current supplying system to provide a biasing current and a current providing method, and particularly relates to a current supplying system providing a constant current at low frequency, an ADC utilizing the current supplying system to provide a biasing current and a current providing method.
2. Description of the Prior Art
Normally, a pipe line ADC (analog to digital converter) utilizes a dynamic biasing circuit as a inside biasing circuit. Based on this structure, the pipe line ADC may have different power for different operating frequencies, such that the power consumption can be optimized. Via such mechanism, the pipe line ADC can operate at different frequencies, such that it is not necessary to design different pipe line ADCs for different operating frequencies.
An ADC always utilized a voltage to current circuit and a constant resistor to generate a constant biasing current. The dynamic biasing circuit utilizes variable resistor to generate different biasing voltages. For example, a switch capacitor circuit can be utilized as the variable resistor. If the capacitors of the switch capacitor circuit is charged and discharged by signals with different frequencies, it can be regarded as a resistor varying corresponding to the frequency. Accordingly, such kind of voltage to current circuit can change the current value corresponding to the frequency.
However, if the frequency of the signal is too low, the capacitor may leak when it is charged. Therefore, the dynamic biasing circuit may lose accuracy when the signal frequency is low.